Metal-air cell with ion exchange material

Abstract

Embodiments of the invention are related to anion exchange membranes used in electrochemical metal-air cells in which the membranes function as the electrolyte material, or are used in conjunction with electrolytes such as ionic liquid electrolytes.

Description

REFERENCE TO PRIOR APPLICATIONS[0001]This application claims priority to U.S. provisional application No. 61 / 498,308 filed 17 Jun. 2011 and U.S. provisional application No. 61 / 568,875 filed 9 Dec. 2011.GOVERNMENT FUNDING SUPPORT[0002]This invention was made with U.S. government support under Contract No. DB-AR-0000038 awarded by the Department of Energy. The government has certain rights in the invention.FIELD OF THE INVENTION[0003]Embodiments of the invention are related to electrochemical metal-air cells using an ion exchange material to facilitate ion transfer between the electrodes, or to assist the ion conductive medium in ion transfer.BACKGROUND[0004]A significant detriment to the energy density of most batteries is posed by the battery's cathode. This is true for battery chemistries using, for example, lithium or nickel. Typically, oxidant is stored at the cathode at a molar charge capacity that is two to five times lower than that of the anode. Many fuel cells, on the other ...

AI Technical Summary

Benefits of technology

[0018]An embodiment of the invention relates to a metal-air cell comprising a fuel electrode for oxidizing a fuel, an air electrode configured to absorb and reduce gaseous oxygen, and an electrolyte that includes an ionic exchange material comprising an ionomer. Another embodiment of the invention relates to an ionically conductive medium for use in an electrochemical cell comprising a fuel electrode and an air electrode for absorbing and reducing gaseous oxygen, comprising: an ionic exchange material comprising a solid ionomer, a salt, and optionally, one or more additives.

Problems solved by technology

A significant detriment to the energy density of most batteries is posed by the battery's cathode.

However, the use of hydrogen and organic fuels precludes high energy efficiencies due to problems with vapor pressure and balance-of-systems complexity, such as humidification and membrane issues.

A limiting factor with conventional metal-air batteries is the evaporation of the electrolyte solution (i.e., the ionically conductive medium), particularly the evaporation of the solvent, such as water in an aqueous electrolyte solution.

Over time, the cell becomes incapable of operating effectively because of the depletion of the solvent.

Indeed, in many cell designs this evaporation issue renders the cell inoperable before the fuel is consumed.

There are other problems associated with conventional aqueous electrolyte batteries, such as water electrolysis during recharging, and self discharge.

In this manner, further aqueous electrolyte is lost from the battery.

Additionally, the electrons that are consumed in reducing hydrogen are not available to reduce the fuel oxide.

Therefore, the parasitic electrolysis of the aqueous electrolyte reduces the round trip efficiency of the secondary battery.

However, either approach adds to both the overall size of the cell, as well as the weight of the cell, without enhancing the cell performance (except to ensure that there is a significant volume of electrolyte solution to offset evaporation of the water or other solvent over time).

But the volume of electrolyte solution in the cell generally does not have a significant beneficial effect on cell performance, and thus generally only detracts from cell performance in terms of volumetric and weight based ratios (power to volume or weight, and energy to volume or weight).

Also, an excessive volume of electrolyte may create a higher amount of spacing between the electrodes, which may increase ohmic resistance and detract from performance.

Ionic liquids which contain a strong Lewis acid such as AlCl3, however, are known to liberate toxic gases when exposed to moisture.

Other problems exist in metal-air rechargeable batteries.

This type of growth during charging may cause the zinc to penetrate through the pores in a porous separator, which may cause short circuiting and battery failure when the zinc contacts the air electrode.

Catalysts or impurities from the air electrode may leach into the electrolyte, which may cause gassing at the metal electrode and degrade the performance of the battery.

This leaching, if persistent over time, may eventually cause the air electrode to break down.

Zincate deposition on the air electrode can cause failure of the battery.

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